1. Field of the Invention
The present invention relates generally to an apparatus for holding a printing cylinder for a printing machine. More specifically, the invention relates to a printing cylinder holding apparatus for a printing machine wherein a cylindrical printing member such as a cylindrical blanket of a blanket cylinder is detachably mounted on the outer periphery of a printing cylinder, the printing member being slidable on the outer periphery of the printing cylinder in axial directions to be put in and out thereof.
2. Description of the Related Art
Japanese Patent Laid-Open No. 6-336004 discloses a blanket cylinder as a printing cylinder for offset press. On the outer periphery of the blanket cylinder, a cylindrical blanket is detachably mounted. The cylindrical blanket is slidable on the outer periphery of the printing cylinder in axial directions to be put on and out thereof.
The blanket cylinder has a pair of shaft portions on both ends thereof. The shaft portions are rotatably supported on a pair of bearing members which are respectively mounted in a pair of frames arranged on both sides of the printing cylinder. In this printing cylinder supporting arrangement, it is required for one of the frames to have an opening for allowing the cylindrical blanket to be put on and out of the blanket cylinder, the both ends of which are supported on the frames.
FIG. 1 shows a conventional printing cylinder holding apparatus. A cylindrical blanket 3 is detachably mounted on the outer periphery of a blanket cylinder 1 so that the cylindrical blanket 3 is slidable on the outer periphery of the blanket cylinder 1 in the axial directions to be put on and out thereof. The cylindrical blanket 3 is provided with a pair of shaft portions 5 and 7 on both ends thereof. The shaft portions 5 and 7 are rotatably supported on right and left side frames 15 and 13 via bearing members 11 and 9, respectively.
The outer diameter of each of the shaft portions 5 and 7 is smaller than that of the blanket cylinder 1. The bearing member 9 for the shaft portion 5 is directly supported on the side frame 13. On the other hand, the bearing member 11 for the shaft portion 7 is supported on the side frame 15 via a sleeve 17 detachably mounted in an opening 19 which is formed in the side frame 15 for allowing the cylindrical blanket 3 to be put on and out of the blanket cylinder 1.
The outer diameter of the bearing member 11 is smaller than that of the blanket cylinder 1, and the inner diameter of the sleeve 17 is smaller than that of the blanket cylinder 1. The outer diameter of the sleeve 17 and the inner diameter of the opening 19 are greater than the outer diameter of the cylindrical blanket 3. The opening 19 is so formed that the its central axis coincide with the rotational axis of the blanket cylinder 1.
The sleeve 17 is provided with a handle 21 for manual operation. When the sleeve 17 is drawn out of the opening 19 by manually operating the handle 21, the opening 19 is open so that the cylindrical blanket 3 can be put on and out of the blanket cylinder 1 through the opening 19 in axial directions.
Japanese Patent Laid-Open No. 6-191007 discloses another type of a printing cylinder holding apparatus. This printing cylinder holding apparatus has a door assembly which is riseably mounted on a frame for opening and closing an opening. On this door assembly, a pair of half-shaped clamping members which are associated with each other for holding a bearing member are movably mounted.
In this printing cylinder holding apparatus, after the clamping members are moved at a loose position by means of a hydraulic cylinder to release the bearing member, when the door assembly is risen by means of another hydraulic cylinder to open the opening, then the cylindrical blanket can be put on and out of the blanket cylinder through the opening in axial directions.
In the conventional printing cylinder holding apparatus as shown in FIG. 1, when the sleeve 17 is intended to be put in the opening 19 again, the blanket cylinder 1 is supported on a single frame 13, so that the axis of the bearing member 11 is shifted from the center of the opening 19 so as to distort the annular space between the outer periphery of the bearing member 11 for the shaft potion 7 and the inner periphery of the opening 19. As a result, it is difficult to put the sleeve 17 in the distorted annular space. It is more difficult to do it when decreasing the gaps between the inner periphery of the sleeve 17 and the outer periphery of the bearing member 11 and between the outer periphery of the sleeve 17 and the inner periphery of the opening 19 in order to precisely support the blanket cylinder. Therefore, it is difficult to easily exchange the cylindrical blanket 3 while precisely supporting the blanket cylinder 1. In addition, it is required to secure a space in which the removed sleeve 17 is stored.
In the printing cylinder holding apparatus as shown in the Japanese Patent Laid-Open No. 6-191007, the clamping members are movably mounted on the door assembly. However, when the axis of the blanket cylinder is shifted from the central axis of the opening, it is difficult to smoothly hold the bearing member of the blanket cylinder again due to the fitting type holding structure of the bearing member.
In addition, this printing cylinder holding apparatus has a quadruplet structure comprising a door, clamping members, a bearing housing and a bearing member. Therefore, the structure is complicated, the door assembly is movable with respect to the frame, the clamping members are movable with respect to the door assembly, and gaps of at least several-hundredths millimeters are required between each movable members. Therefore, due to plays between the respective movable members, it is difficult to precisely support the blanket cylinder and to precisely rearrange the printing cylinder holding portion after the printing member is detached. It is also difficult to maintain the required accuracy for the printing cylinder holding apparatus, since shape error such as out-of-roundness of each members, dimensional error and assembly error are integrated to reduce the supporting and rearranging accuracy of the blanket cylinder.